Exhaust gas treatment devices such as catalytic converters and particle filters feature a casing, e.g., of cylindrical shape. At least one exhaust gas treatment cartridge is arranged in the casing, and a funnel is provided on at least one axial end of the casing. In the manufacture of the exhaust gas treatment device, it is possible, in principle, to initially insert the respective exhaust gas treatment cartridge that comprises, in particular, a particle filter element or a catalytic converter element axially into the casing that is open on both sides, wherein the inside cross-section of the casing initially is larger than an outside cross-section of the exhaust gas treatment cartridge. In order to fix the exhaust gas treatment cartridge within the casing in the finished exhaust gas treatment device, the cross-section of the casing can be reduced such that the inside cross-section is equal to the outside cross-section of the exhaust gas treatment cartridge along its entire length. This sizing process simultaneously makes it possible to compress a supporting mat of the exhaust gas treatment cartridge that is wrapped around the circumference of a cartridge body (particle filter element or catalytic converter element) of the exhaust gas treatment cartridge in order to generate a pre-stress. After this sizing process, a funnel is selected that corresponds to the ultimate inside cross-section of the casing after the reduction in cross-section, wherein the outside cross-section of the funnel should match the aforementioned ultimate cross-section as closely as possible, but be smaller than this ultimate cross-section in order to allow an unproblematic insertion of the funnel into the respective end region of the casing. The funnel is subsequently fixed on the casing in a gas-tight fashion, particularly with the aid of a circumferential welding seam.
Since the exhaust gas treatment cartridges and their cartridge bodies are subject to manufacturing-related dimensional tolerances, the reduction of the casing cross-section, i.e., the sizing process, results in varying ultimate cross-sections of the casing. Since the radial gap between the funnel and the casing should be as small as possible in order to easily produce the welding seam between the funnel and the casing, it is necessary to make available a relatively broad selection of funnels with different cross-sections. This is associated with a relatively high expenditure. In addition, the ultimate cross-section of the casing needs to be measured after the sizing process in order to select a suitable funnel. The measuring of the ultimate cross-section, as well as the selection of an appropriate funnel, is time-consuming and therefore cost-intensive.